The American Airlines pilots union confronted Boeing over possible safety issues in the 737 Max prior to the Ethiopian Airlines plane crash in March, audio recordings from a November 2018 closed-door meeting between the pilots and Boeing executives reveal.

Both crashes are believed to have been caused by a malfunctioning sensor that sent faulty data to the planes’ anti-stall systems, forcing them to go down. Boeing planes worldwide have been grounded following the deadly incidents. The company is currently in the process of updating its planes’ anti-stall system, known as MCAS.

But at the time of the meeting on Nov. 27, Boeing executives at the meeting resisted the pilots’ calls for urgent action, according to the recordings. Mike Sinnett, a Boeing vice president, said during the meeting that it was unclear whether the malfunctioning anti-stall system was the sole cause of the Lion Air crash off Indonesia, in which 189 people were killed, the New York Times reports.

“No one has yet to conclude that the sole cause of this was this function on the airplane,” he said, according to the recording. Boeing did not immediately respond to a request for comment.

Officials said they would make software changes, but that they didn’t want to rush the process, CBS reports.

“We want to make sure we’re fixing the right things,” one official said in the meeting, according to CBS. “That’s the important thing. To make sure we’re fixing the right things. We don’t want to rush and do a crappy job of fixing the right things, and we also don’t want to fix the wrong things.”

The software fixes had not gone through by the time a second 737 Max crashed in Ethiopia in March, killing all 157 people on board.

Boeing now faces rigorous questioning over its handling of the aftermath of the crashes and for its design of the 737 Max jets. Multiple probes have been opened into Boeing’s handling of the plane’s production and the Federal Aviation Administration’s oversight.

On Wednesday, a Congressional committee will question the Federal Aviation Administration, over the certification of the 737 Max. FAA acting administrator Daniel Elwell will face questions from the House Transportation Committee on the administration’s role in approving the jet to fly, the Times reports. National Transportation Safety Board chairman Robert Sumwalt will also appear at the hearing, which marks the first among several planned by House Democrats on the 747 Max plane.

Federal grand jury subpoenas have also been issued to pilots unions representing American Airlines and Southwest Airlines for documents related to the 737 Max. Southwest will cooperate with the request, Bloomberg reports. The Allied Pilots Association, which represents the American Airlines pilots, did not immediately respond to a request for comment.